Peter Salk gets a polio shot from his father in the spring of 1953, as his mother looks on. Jonas Salk assured the public that he’d vaccinated his own family first, adding, “I will be personally responsible for the vaccine.” (March of Dimes)

It started out as a head cold. Then, the day before Halloween, 6-year-old Frankie Flood began gasping for breath. His parents rushed him to City Hospital in Syracuse, New York, where a spinal tap confirmed the diagnosis every parent feared most in 1953: poliomyelitis. He died on his way to the operating room. “Frankie could not swallow—he was literally drowning in his own secretions,” wrote his twin sister, Janice, decades later. “Dad cradled his only son as best he could while hampered by the fact that the only part of Frankie’s body that remained outside the iron lung was his head and neck.”

At a time when a single case of Ebola or enterovirus can start a national panic, it’s hard to remember the sheer scale of the polio epidemic. In the peak year of 1952, there were nearly 60,000 cases throughout America; 3,000 were fatal, and 21,000 left their victims paralyzed. In Frankie Flood’s first-grade classroom in Syracuse, New York, eight children out of 24 were hospitalized for polio over the course of a few days. Three of them died, and others, including Janice, spent years learning to walk again.

Then, in 1955, American children began lining up for Jonas Salk's new polio vaccine. By the early 1960s, the recurring epidemics were 97 percent gone.

Salk, who died in 1995, would have turned 100 on October 28. He is still remembered as a saintly figure—not only because he banished a terrifying childhood illness, but because he came from humble beginnings yet gave up the chance to become wealthy. (According to Forbes, Salk could have made as much as $7 billion from the vaccine.) When Edward R. Murrow asked him who owned the patent to the vaccine, Salk famously replied, “Well, the people, I would say. There is no patent. Could you patent the sun?”

I recently spoke with Salk’s oldest son, Peter, an accomplished medical researcher in his own right who spent years working alongside his father at the Salk Institute for Biological Studies. Peter told me about his father’s late-in-life HIV research and the ethical concerns he explored in such books as Man Unfolding and The Survival of the Wisest. Peter also spoke with impressive thoughtfulness about today’s anti-vaccine movement and reflected on why so many Americans came to distrust life-saving vaccines such as the one his father helped bring to the world.

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Jennie Rothenberg Gritz: What sort of person was your father?

Peter Salk: He was a kind person. He really cared about people. In his personal interactions, he did everything he could to uplift whomever he was interacting with. As things went on with polio, there was obviously a great deal of controversy. But he wasn’t one who wanted to engage in battles, even when people attacked him for the approach he was taking.

Rothenberg Gritz: What gave him the confidence to keep working on his vaccine when so many people were telling him it couldn’t be done?

Salk: That was sort of his nature. He just didn’t accept dogma if he didn’t understand it. When he was in medical school, taking a course in microbiology, the professor spoke about two bacterial diseases—tetanus and diphtheria—that are caused by toxins that bacteria produce. You can inactivate those toxins chemically and use them to produce a protective immune response. In the next lesson, the professor said that when came it to viral illnesses, you couldn’t do that. You needed to have a living virus to induce immunity that would protect against the disease. My father didn’t understand why one thing would be true for a couple of bacterial diseases but not for viral ones. He thought you ought to be able to do same thing with a virus: inactivate it and then induce an immune response without any risk of the vaccine causing the disease itself.

Rothenberg Gritz: A lot of people thought Albert Sabin’s live-virus vaccine was the better way to go, right?

Salk: Yes, Albert Sabin was an established figure in the field. He was not one to welcome someone with different views about things. And indeed, most people felt that his oral vaccine, where you use a weakened version of the live virus, was going to be the most effective.

Polio gets into the body through the mouth and then grows in the intestines. Sometimes it will travel into the blood stream, then into the nervous system. It’s there—in the spinal cord or the brain—that the virus causes paralysis. To be protected against paralysis, all you need are antibodies circulating through the bloodstream. That’s the kind of protection my father’s injectable vaccine provides.

But in 1962, the Sabin oral vaccine was introduced on a wide scale. It ultimately replaced the injected vaccine in this country entirely. The problem with the Sabin vaccine is that the weakened virus can revert back to a dangerous form in some people. As a result, the wild polio virus was completely gone at the end of the 1970s, but for decades we continued to have somewhere between 8 and 12 cases each year that were caused by the vaccine itself.

In this country, the decision was finally made in 2000 to go back to the injectable vaccine. On a global level, there was an eradication initiative that started in 1988. They primarily used the oral vaccine. By 2012, the number of reported, naturally occurring polio cases was down from about 350,000 in 1988 to 223. But the WHO estimates that something on the order of 250 to 500 cases of polio are caused every year by the live vaccine itself.

Rothenberg Gritz: People have been concerned by the idea that vaccines can cause disease in healthy children.

Salk: There are some subtleties to this. With pertussis, for instance, the old vaccine was based on using the whole killed organism. That was very effective, but because there were a whole lot of different kinds of proteins that were all mixed up, there were some side effects. Later on, they developed a so-called acellular pertussis vaccine, where you use purified materials from the bacterium. It doesn’t produce as strong or long-lasting an immune response—people need to have booster shots when they’re adults, for instance. But it doesn’t cause the same side effects.

When my own son Michael was born 31 years ago, the whole-cell vaccine was still in use. Whooping cough was essentially gone in this country by that time, so from one perspective, why should we take the risk of causing a high fever or other side effects in our own child? I know I certainly thought about this a lot. But I just couldn’t bring myself to take advantage of the good that other people had done by immunizing their kids—to take a free ride, so to speak. Michael did end up developing a fever. But I couldn’t have lived with my decision if we hadn’t given him the vaccine.